This device is rooted out-of-the-box and it has unlocked bootloader. Stock recovery also allows flashing zips that are signed with generic test key. I haven’t found a way to use adb when connected with an USB cable. There’s no way to boot the device into bootloader to use fastboot either. There’s still about a dozen ways to install TWRP - here’s a few.

Booting from SD card:

Download recovery-twrp3020-nexbox_a95x.img and rename it as recovery.img